Digital hearing devices are known in the art. Such a device typically comprises a microphone, a preamplifier, an analog-to-digital converter (ADC), a signal processor, a digital-to-analog converter (DAC) and a speaker connected to form an audio signal path. A known problem with such hearing devices is that the dynamic range of the ADC is typically chosen less than the dynamic range of acoustic signals generally encountered in order to reduce the power consumption of the ADC. This reduction is especially important in hearing devices, such as hearing aids, intended for being worn at or in an individual's ear where the space for batteries is generally limited.
It is further known to increase the dynamic range of the hearing aid without increasing the power consumption of the hearing device by varying the gain of the preamplifier depending on the level of the microphone signal. Since clipping substantially increases distortion of the digitised signal, the gain is reduced when loud signals are received and vice versa. Thus the hearing device may reproduce e.g. speech signals with high quality both when the speaking person is close-by and when he or she is further away from the wearer.
Technical progress has led to ADC's which have low power consumption and at the same time have dynamic ranges nearly large enough to comprise the dynamic range of typical acoustic signals. A reduction of the preamplifier gain thus need only be applied when very loud signals are received, and it is therefore a known solution to temporarily reduce the preamplifier gain with fast attack and release times when a clipping of the amplified signal during digitising is expected.
The above approaches do, however, not provide a completely satisfactory signal quality. On one hand, the attack time needs to be short enough to prevent clipping in the event of transients, e.g. noise produced by hand-clapping or cutlery hitting a plate, and the release time should not be too long in order to allow the individual to hear speech and other sounds following such a transient. On the other hand, if too short attack and release times are chosen, the gain changes themselves produce audible distortion of the digitised signal. Furthermore, if a long release time is chosen in order to reduce the latter distortion, the gain changes may instead cause so-called “pumping”, i.e. a noticeable and annoying level variation following the transient. The pumping will be increased if the hearing device applies dynamic range compression, which is typically the case in hearing aids in order to compensate for recruitment.
It is an object of the present invention to provide a hearing device without the above disadvantages.
It is a further object to provide a method for operating a hearing device which allows the hearing device to operate without the above disadvantages.